1. Field of the Invention
The present invention relates to a device and a method for determining the magnetic field strength of an electromagnet.
2. Discussion of the Prior Art
The strength of the magnetic field of an electromagnet can be determined by measuring the current flowing through the magnet, since this current is a direct measure of the magnetic field that is produced, although this is corrupted in a magnet with an iron core inter alia by hysteresis and saturation effects. In electromagnets which are used in accelerator installations, very high currents frequently occur, so that the magnetic field which occurs around a supply line is used for measurement. So-called direct-current current transformers (DCCTs) are known for this purpose from the prior art, as disclosed by way of example in WO 2005/052605. Alternatively, it is also possible to measure the magnetic field in the magnet directly with the aid of a Hall probe.
However, measurement devices such as these have the disadvantage that changes which occur in the current and/or the magnetic field become evident in the output signal only after a comparatively long time. It is therefore frequently not possible to react sufficiently quickly to changes in the magnetic field. This is particularly relevant in the case of magnets for accelerator installations since in this case even small discrepancies between the magnetic field strength and the nominal value lead to deflection or defocusing of the beam, and are therefore associated with the beam striking elements of the beam line. The latter in turn results in gamma and neutron radiation being produced, so that the area around the accelerator is subject to an increased radiation load. Furthermore, the beam line elements may be damaged. In order to avoid such radiation loads and damage, it is therefore of particular interest to detect even minor changes in the magnetic field as quickly as possible.
This problem of the known magnetic field measurement devices is associated with the peak value, defined with respect to a reasonable measurement time, of the sum of the noise and disturbance signals in the output signal in the frequency range up to 10 kHz being about 10−4 with respect to full deflection. The disturbance signals may in this case, for example, be created by switching heavy loads in the surrounding area, adjacent power electronics or interference spikes on the supply network. However, a peak value such as this during operation of acceleration installations is excessive since limit values must be set there such that the accelerator is switched off if these limit values are exceeded just once, with these limit values being in the order of magnitude of the peak values above. Otherwise, there can be no assurance that defocusing and unacceptable deflection will not occur.